1. Field of the Invention
The present invention generally relates to the field of antennas, for example, but not limitatively, for use in mobile telecommunications like mobile telephony networks, and particularly to methods for designing antennas for, e.g., telecommunications systems. More specifically, the invention relates to a method for synthesizing array antennas.
2. Description of Related Art
As known in the art, an array antenna is an antenna formed of a plurality of equal radiating elements, arranged to form an array, which are fed by signals that are in proper amplitude and phase relationship with one another.
In order to design an array antenna, designers often have to synthesize the so-called “radiation diagram”, or “radiation pattern” of the antenna, in such a way as to comply with design prerequisites.
Several methods are known in the art for synthesizing the radiation pattern of array antennas. Examples of known methods are the Dolph-Chebyshev method, the Taylor method, the Fourier series method, and the Woodward-Lawson method, just to cite some.
Without entering into excessive details, well known to those skilled in the art, the Dolph-Chebyshev method and the Taylor method allows the designer setting a level for the secondary lobes (the secondary lobes height affects the width of the primary lobe); in greater detail, the Dolph-Chebyshev method aims at achieving a radiation pattern having secondary lobes of equal amplitude, whereas the Taylor method is aimed at achieving a radiation pattern with secondary lobes whose amplitude is below a predetermined level. The Fourier series method tries to generate the desired radiation pattern exploiting the Fourier transform relationship between the coefficients of the signals feeding the antenna's radiating elements and the radiated electromagnetic field; the Woodward-Lawson method tries to reproduce the target radiation pattern as a superposition of elementary beams generated by uniform sub-arrays of radiating elements.
A description of the above (and other) array antenna synthesis methods is provided in R. J. Maiiloux, “Phased Array Antenna Handbook”, Artec House, Norwood, Mass., 1993, pp. 17-19 and 112-136.
In S. Takubo et al., “Radiation Pattern Synthesis of an Unequally Spaced Array Antenna”, IEEE Antennas and Propagation International Symposium, Jul. 16-21, 2000, Salt Lake City, Utah, a radiation pattern synthesis method for an unequally spaced array antenna is proposed that employs the LMS (Least Mean Square) method. Design examples for the objective radiation pattern [A] (amplitude and phase) of −25 dB Chebyshev pattern are described.